Most winged aircraft conventionally have had control surfaces, such as flaps, to control various flight characteristics of the aircraft. Communication is provided between the pilot and the control surfaces, including mechanical actuation systems. In most modern aircraft, mechanical actuation systems for aircraft flight control surfaces often are required to provide a backdrive or "blowback" under air loads in the event of hydraulic system failure. A backdrive position is an aerodynamic neutral panel position which allows the aircraft to continue flight operations until a safe condition exists, such as until a safe landing can be attained.
The rate at which a panel or flight control surface blows back, how close it gets to neutral position, and its flutter resistance once it gets to the neutral position, all are concerns of the aircraft industry and related agencies. Heretofore, complex control systems involving mechanical linkages, screw actuators, complex hydraulic circuitry and the like have been used to provide actuation systems allowing backdriving of the control surfaces and preventing surface flutter at neutral position.
In some instances, a clutch is provided between a motive means and the control surface(s), and in other instances a brake is provided between the motive means and the control surface. Prior complex backdriving systems may operate through either of these components.
The present invention is directed to providing a very simple hydraulic backdrive system for aircraft flight control surfaces which use either a clutch or a brake between the motive means and the flight surface.